[FFmpeg-devel] [PATCH] avcodec/webp: avoid trying to decode trailing junk in bitstreams

[Pascal Massimino]

Michael,

On Thu, Sep 5, 2019 at 6:20 PM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> On Wed, Sep 04, 2019 at 07:43:15AM +0200, Pascal Massimino wrote:
> > Hi,
> >
> > this patch break the decoding loop when invalid webp chunk is
> encountered.
> > We can still have a valid frame ready to be returned (*got_frame = 1).
> >
>
> > fixes trac #8107 (/#7612)
>
> These bug references should be in the commit message
>

done, new patch attached.


>
>
> >
> > skal/
>
> >  webp.c |    7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 2d80b062adade6044f64a00838b55f9427cc1f73
> 0001-webp-fix-decoding-for-trailing-junk.patch
> > From 9edff4f9812fad7f605bdc12954f82a8745a25ee Mon Sep 17 00:00:00 2001
> > From: Pascal Massimino <pascal.massimino at gmail.com>
> > Date: Wed, 28 Aug 2019 09:41:42 +0200
> > Subject: [PATCH] webp: fix decoding for trailing junk
> >
> > some bitstream have trailing junk, despite being valid webp data.
> > In case of apparent error, abort the loop and let *got_frame
> > decide whether this is an error or not.
> > Another possibility would be turning the loop into:
> >     while (!*got_frame) {...}
>
> what is that trailing junk ?
>

As mentioned in the trac description, one frequent source of such junk
is padding of encrypted packets (or, just, left-overs).


>
> i would guess its not a known chunk but rather hits the default
> is that just a bunch of 0 or 0xFF bytes ?
> detecting before we read into the end feels more robust if
> we can simply detect the "junk"
>

As i mentioned in the description, a possibly more robust solution would be
just stopping the loop as soon as 'chunk_size' bytes have been consumed
(leading to *got_frame = 1) and no more. This current patch is minimalist,
though.

skal/





>
> thanks
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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